Method for producing gelatin

ABSTRACT

In a method for producing gelatin from collagen-containing raw material, the raw material is ground and mixed with water to form a slurry; the slurry is treated with an acid and heated in order to expose the collagen in the raw material; the pH and the temperature of the slurry are adjusted once more; the slurry is separated into a liquid portion and a solid residue; and the gelatin is recovered from the liquid portion.

This invention relates to a method for producing gelatin from acollagen-containing raw material.

Gelatin is a natural product that is used primarily in the foodindustry, but also in the pharmaceutical, the photographic, the textileand the paper industry.

Gelatin is a protein obtained from collagen that occurs in the skin,connective tissue, bones and other parts of animals, mammals as well asfish. In the bone phase, the collagen is present in the form of afibrous matrix surrounded by inorganic material. When looking atsuitably-colored bone phase under the microscope, one sees that the bonephase is crisscrossed by densely-packed bundles of collagen fibres.Under an electron microscope, these fibres are seen to consist offibrils that are about 400-1200 Å in diameter. The fibrils have across-striped structure similar to that of connective tissue. Onaverage, collagen makes up almost a third of the bone phase, based ondry weight. The inorganic phase consists of small, densely-packedcrystals (50×600 Å) having an X-ray diffraction pattern similar to thatof hydroxyapatite, 3.Ca₃ (PO₄)₂.Ca(OH)₂.

The collagen fibrils are composed of rod-shaped collagen molecules(tropocollagen) having a length of 300 nm and a thickness of 1.5 nm. Thetropocollagen is composed of three polypeptide chains, so-calledα-chains, forming a triple helix. In the fibrils, the tropocollagen iscross-linked by covalent bonds primarily located at the molecule ends,the so-called telopeptides. Native tropocollagen is highly resistant toalkaline, acid and enzymatic hydrolysis, owing to its densely-packedhelix structure. However, the telopeptides do not have such a highresistance, since they are not integrated in the helix structure, butmay be regarded as randomised or globular regions.

When the collagen molecule is heat-denatured, the triple helix isuntwined, and free polypeptide chains are formed, i.e. gelatin isobtained. When the collagen molecules are present in such tissue as bonetissue, the situation is more complex. In order that the tropocollagenmolecules should be dissolved and heat-denatured to gelatin, thecovalent cross-links between the molecules have to be broken up. Thiscan be brought about e.g. by high-temperature heating (autoclaving).However, such heating not only breaks up the cross-links, but alsocauses random hydrolysis of the bonds in the tropocollagen, resulting ingelatin of poor quality. In the method most commonly used, thetelopeptides and, hence, the cross-links are hydrolysed at a lowtemperature (15°-25° C.), leaving the triple helix intact and renderingthe tropocollagen extractible.

In conventional techniques for producing gelatin from bone, the wholebones or bones divided into pieces are first demineralized completelywith acid at a low temperature and for several days, so that thecollagen matrix is exposed and ossein is obtained. Demineralization,which is performed in a separate step, implies treatment at a pH<2, inwhich large amounts of acid are consumed. Separate and completedemineralization is an extremely important part of today's gelatinproduction on the basis of bone raw material. The purpose of suchdemineralization is to dissolve the calcium salts in the bone, therebyto expose the collagen matrix. Calcium is present in the form ofhydroxyapatite, which is dissolved by treatment with dilutedhydrochloric acid. After demineralization, the ossein is "conditioned"by means of alkali, such as lime or lime milk, for 1-6 months at a lowtemperature. In this treatment, the intramolecular bonds are broken up,the solution is neutralised and the collagen is extracted at an elevatedtemperature (50°-95° C.). The collagen is denatured, and gelatin isobtained.

Present-day methods for producing gelatin distinguish between whetherthe raw material employed is bone or hide (split, rind) and otherconnective-tissue material.

Containing no minerals, hide and connective tissue are not subjected toany demineralization, but are otherwise treated in the same way as boneraw material.

Alternatively, "conditioning" may imply acid treatment, which meansthat, after being washed and optionally divided into smaller pieces, theraw material is left in an acid bath for 1-4 days at a low temperature.Also the acid conditioning takes place at a pH<2. The type ofpretreatment employed chiefly depends on the origin of the raw material.Ossein, calf and cattle hides are primarily treated according to thealkaline method, whereas bacon rind is especially suited for the acidmethod owing to its high fat content. Furthermore, old hides requiretreatment according to the alkaline method, on account of the manycross-links found in such material. In the case of younger hides, theacid method may well be used.

The alkaline treatment, in which ossein and/or hide material are treatedfor a long time (up to 6 months) with lime or lime milk (pH about11-12), requires extremely large amounts of process water and chemicals,since the water has to be changed several times. Thus, up to 1000 l ofwater may be needed to produce 1 kg of gelatin. Moreover, the treatmentwith lime is followed by deliming, which also is a complex method step.

Although the acid treatment is not as time-consuming as the alkalinetreatment, one or a few days are nevertheless needed to expose most ofthe collagen.

Furthermore, conventional techniques require a great number ofextraction steps (up to 6 or 7) to yield an acceptable result. Thequality of the gelatin obtained is not homogeneous, but generallydeteriorates with the number of extraction steps. High-quality gelatinis obtained in the first steps only.

Thus, the drawbacks of conventional methods chiefly reside in theextremely long treatment times and the considerable amounts of processwater and chemicals required, resulting in large amounts of waste andassociated environmental problems. A further drawback is that differentraw materials require different treatments. Naturally, the longtreatment times have an adverse effect on the quality and the yield ofgelatin.

German Patent Specification 27 47 798 discloses a method for extractingcollagen from sinews and hides and then processing the collagen toproduce gelatin. In this method, alkaline treatments alternate withdifferent washing stages for recovering collagen from the raw materialemployed. Considerable amounts of process water are supplied and drawnoff during implementation of the method, resulting in large amounts ofwaste and associated environmental problems, as indicated in theforegoing. Furthermore, the German method can only be applied to sinewsand hides.

EP-B1-0 323 790 describes a method for producing gelatin from bone meal.Like other prior-art methods, this method includes different washingsteps which, however, alternate with acid treatments. Thus, also thismethod yields large amounts of process water with ensuing environmentalproblems.

Depending on the field of application, different quality requirementsare placed on the gelatin. Gelling capacity and gel strength are twoimportant properties of gelatin. Conventionally, gel strength isindicated in Bloom numbers. Thus, a Bloom number of>about 240 indicateshigh-quality gelatin, a Bloom number of about 120-240 indicatesaverage-quality gelatin, and a Bloom number of<about 120 indicateslow-quality gelatin.

Accordingly, it is a desideratum to provide cost-effective andenvironmentally-friendly production of high-quality gelatin, which wouldinvolve shorter residence times, less process water and chemicals and,hence, less waste.

One object of the invention is to provide a cost-effective andenvironmentally-friendly method for producing high-quality gelatin.

Another object of the invention is to provide a method for producinggelatin, which can be used for different sorts of collagen-containingraw material as well as mixtures of such materials.

According to the invention, these objects are achieved by a method forproducing gelatin from a collagen-containing raw material, comprisingthe steps of

a) grinding the raw material to a particle size not exceeding 1 mm,

b) mixing the ground raw material with water to form a slurry,

c) subjecting the slurry from step b), in optional order, to anadjustment of the pH to 2-5 and to an adjustment of the temperature to60°-130° C. for a time of from 1 s to 1 h,

d) adjusting the temperature of the slurry once more,

e) separating the slurry into a gelatin-containing liquid portion and asolid residue,

f) adjusting the pH of the slurry or the liquid portion before or after,respectively, the separation, and

g) recovering the gelatin from the liquid portion in filtration stepsand/or other cleaning steps, with essentially no removal of processwater in steps a)-f).

The inventive method can be applied to different collagen-containingmaterials, such as hides, split, rind, gristle, sinews, intestines,stomachs, connective-tissue material and different types of bonematerial from animals.

The inventive method may also include a partial demineralizationtreatment and/or an enzyme treatment in order to improve the yield evenfurther. If so, such treatments are carried out prior to step c).However, a good yield is obtained also without any such additionaltreatments. Optionally, the raw material employed can be defatted priorto grinding.

If an enzyme treatment involving pH and temperature adjustments is to becarried out prior to step c), the pH of the slurry of ground rawmaterial should first be adjusted to the proper pH of the enzymeemployed, thus preventing denaturation of the enzyme due to an improperpH.

The inventive method for producing gelatin can be implemented incontinuous or semicontinuous fashion as well as batchwise.

The method according to the invention is schematically illustrated inFIG. 1. Any collagen-containing raw material may be used. To begin with,the raw material is ground to a suitable particle size. Then, theparticles are slurried, and the resulting slurry is acidified by theaddition of an acid and is heated, the elevated temperature beingmaintained for a certain period of time. Thereafter, the treated slurryis cooled, and solid material is separated from the gelatin-containingliquid portion. In order to increase the pH, a base is added to theliquid portion under agitation, and the gelatin-containing solution isthen processed and cleaned according to prior-art techniques, so as toform a gelatin solution. It is only at this stage that process water isseparated from the production.

The base added in order to raise the pH after the acid treatment mayfurther be added before the separation of solid material instead ofafter.

The method according to the invention will now be described in moredetail.

The raw material employed is obtained e.g. from slaughterhouses,meat-cutting centres or the fish industry. By "collagen-containing rawmaterial" is here meant unmixed as well as mixed collagen-containing rawmaterial. The raw material employed may be one or a few of the materialsmentioned above, originating from all types of mammals as well as fish.

The collagen-containing raw material is ground to an average particlesize not exceeding 1 mm. The grinding, either wet grinding or drygrinding, is performed in one or more steps with the aid of suitable,conventional equipment. The average particle size should be about 1 mmat the most, preferably about 300 μm at the most. An average particlesize of<100 μm is especially suitable, and an average particle sizeof<40 μm is most preferred. Optionally, the material may be defattedprior to grinding, e.g. to a fat content not exceeding 3% by weight.Although such a step is not critical, a low fat content facilitatessubsequent process steps.

The ground material is mixed with water to form a slurry, and the pH andthe temperature are then adjusted in optional order. The pH is suitablyadjusted to 2-5, preferably 3.5-5. The temperature suitably is 60°-130°C., preferably 80°-110° C. The slurry is kept at this temperature for aperiod of time in the range of from 1 s to 1 h, preferably in the rangeof 5-40 min, and most preferred in the range of 10-30 min. The pH, thetemperature and the time are determined according to the degree ofgrinding and the quality requirements placed on the gelatin to beproduced.

The amount of collagen converted to gelatin increases proportionately tothe reduction of particle size, the decrease in pH, the increase intemperature and the prolongation of the residence time. However, themore extensive the treatment to which the material is subjected, thelower the quality of the resulting gelatin. Thus, these parameters haveto be so combined that the aimed-at gelatin quality is obtained. In someapplications, lower-quality gelatin may, of course, do.

After grinding, the material may optionally be subjected to a brief andpartial demineralization and/or an enzyme treatment in order to enhanceproduction efficiency and increase the total yield of gelatin. Thepartial demineralization is performed with an acid, such as phosphoricacid. The enzyme treatment may be performed with one or more enzymes, ora mixture of enzymes. Different proteolytic enzymes have differentspecificities for different amino acid sequences, as well as differentpH- and temperature-dependence. Examples of suitable enzymes arealkaline, bacterial proteases. In the enzyme treatment, the pH of theslurry is adjusted to a suitable pH in view of the enzyme employed. Aspecific example of an enzyme that may be used is ESPERASE® (Novo,Denmark), which requires a pH of about 7. Conveniently, no more than aper cent or so of the enzyme is added, e.g. 0.5%. The enzyme in theslurry is allowed to act a few hours at room temperature, and thecollagen is then extracted from the slurry at an elevated temperature,as above.

The pH is adjusted by means of an acid, such as hydrochloric acid,phosphoric acid, sulphuric acid, nitric acid or acetic acid. It is notof decisive importance which acid is used in the inventive method, butbasically all acids may be employed, including organic as well asinorganic acids and mixtures thereof. Some acids are, however, moreeffective than others. It may be advantageous to use phosphoric acid inorder to decrease the pH and to use calcium dihydroxide in order toincrease the pH, since these two acids form a type of calcium phosphatethat is a natural ingredient of bone material. It is less expensive touse hydrochloric acid and sodium hydroxide, but the final gelatinsolution obtained after the separation will then have a higher saltcontent.

As to the temperature adjustment at this stage of the inventive method,the reaction rate increases with the temperature. There is basically nomaximum temperature, but the organic material is rapidly decomposed atvery high temperatures. The residence time required will then beextremely short and difficult to regulate at such high temperatures.

If low-quality gelatin, such as bone glue, is an acceptable or aimed-atproduct, the temperature may, of course, be increased in order to reducethe residence time.

The residence time is achievable in a conduit system through which theslurry is pumped or in a tank where the slurry is kept for a certainperiod of time. However, this last embodiment implies that differentparts of the slurry will have different residence times, and thisembodiment therefore should not be used in the case of extremely shortresidence times.

After this treatment, the temperature is adjusted in order to completethe reaction. Conveniently, the temperature is adjusted to 100° C. atthe most, for instance to 60° C.

After this temperature adjustment, the slurry is separated into a liquidportion and a solid residue. The liquid portion contains the gelatinrecovered from the collagen. Depending on the raw material employed, thesolid residue contains undissolved bone, salts, insoluble proteins, andso forth. Preferably, the solid residue is washed in order to recover asmuch gelatin as possible. The separation can be carried out in aconventional decanter, but other conventional equipment may of course beused.

The pH should also be adjusted when the need arises. This can be doneeither before or after the separation of the slurry into a liquidportion and a solid residue. The pH suitably is 5.5-6.0, for instance5.5. Various alkaline chemicals may be used for adjusting the pH at thisstage. As mentioned in the foregoing, calcium hydroxide isadvantageously used, and it is generally an advantage to use an alkalinechemical reacting with the acid to form an insoluble substance. As aresult, the gelatin solution produced will have a lower salt contentthan it would have had if the chemicals had not reacted with oneanother. The temperature and pH adjustments performed in this step aredesigned to strike a balance between decomposition and microbiologicalactivity. Since gelatin gels at about 30° C., it is vital that thetemperature be maintained well above this temperature for the remainderof the process.

The resulting gelatin solution may be used as such, with the yield andthe quality obtained, but the solution may also undergo additionaltreatment and cleaning steps. If the solids are remixed with water andhomogenised and then subjected to yet another pH adjustment to a pH of2-5 as well as a temperature adjustment to 60°-130° C. for a period oftime ranging from 1 s to 1 h, to be followed by cooling, etc., the yieldcan be increased even further. Naturally, this process can be repeatedany number of times. The solid residues from these steps are driedseparately.

The gelatin-containing liquid portion may then be further treated inorder to recover dry gelatin. Depending on the aimed-at gelatin quality,the gelatin solution undergoes different filtration steps and/or othercleaning steps. Also, the different filtration and cleaning steps dependon the raw material employed. A few examples of filtration and cleaningsteps are given below.

The solutions obtained from the different decanting steps are mixed andfiltered, e.g. by two different filters, in order to remove particlesand coarse material. For instance, 50-μm and 25-μm filters may suitablybe used. In order to produce high-quality gelatin, it is necessary toremove salts and peptides, which is best done by ultrafiltration, whichalso concentrates the solution. Generally, ultrafiltration does notremove all the salts, but ion exchange may be needed to achieve asufficiently low salt content. After these steps, the solution may stillbe cloudy and have a certain taste. If the solution contains fat, thiscan be removed with the aid of special fat-absorbing filters. Color canbe removed by active-carbon filtration, and final clarity can beobtained by filtration through a fine filter.

Being of conventional design, the equipment used in the different stepsof the inventive method will not be described in more detail here. Also,the choice of appropriate equipment is a measure of convenience obviousto those skilled in the art.

The present inventions yields high-quality gelatin, generally having aBloom number above 250, while involving low costs, short process-timesand small process volumes, as compared with the prior-art methodsmentioned in the foregoing. Thus, the inventive method for producinggelatin is cost-effective as well as environmentally-friendly. Comparedwith the above prior-art methods for producing gelatin from bone rawmaterial, the inventive method is especially advantageous in dispensingwith the separate step of complete demineralization as well as the longresidence time of alkaline conditioning. Furthermore, no or practicallyno process water is drawn off from the process until the slurry has beenseparated into a gelatin-containing liquid portion and a solid residueand the pH has been adjusted. In the method according to the invention,the collagen molecules are exposed in different fashion.

The method according to the invention may be implemented in one step,i.e. continuously, which is unfeasible with prior-art methods owing tothe long residence times. Moreover, the gelatin solution obtained afterthe separation step in the inventive method is fully acceptable asregards yield as well as quality. Most prior-art methods, on the otherhand, require up to 6 or 7 extraction steps to give the same yield. Theinvention also has the considerable advantage of enabling use of one andthe same method, regardless of the origin of the raw material employed,as well as the use of unmixed or mixed raw material.

Another considerable advantage associated with the invention is that theamount of waste leaving the process in the form of process water isinsignificant, compared with prior-art methods. Naturally, thisautomatically enhances cost effectiveness.

The invention will now be illustrated in more detail with the aid of afew non-restricting Examples.

EXAMPLE 1

This Example involves a continuous method. Bone of food quality obtainedfrom slaughterhouses was defatted in an Alfa Laval Centribone processand wet-ground to an average particle size of 80 μm, water being addedin such an amount that a slurry having a dry solids content of 20% byweight was obtained. The pH of the slurry was adjusted to 3.5-by meansof phosphoric acid. Then, the slurry was heated to 110° C. in an ALFALAVAL-CONTHERM® scraped-surface heat exchanger, and the slurry was keptat this temperature for 15 min in a conduit system. After 15 min, the pHwas adjusted to 5.5 by means of calcium dihydroxide.

Thereafter, the temperature was adjusted to 60° C. in ALFALAVAL-CONTHERM®. The slurry was then transferred to an Alfa Lavaldecanter NX409, where the solids were separated from the water. Thesolids were mixed with fresh water at a temperature of about 60° C. to ahomogeneous slurry, which was transferred to another decanter. Theliquid portion obtained in this treatment was mixed with the liquidportion obtained in the first treatment. About 75% of the collagen hadbeen converted to gelatin in this treatment. By using two decanters,about 80% of the gelatin was recovered to the liquid portion. Theresulting solution, which consisted of the mixed liquid portions, wasfiltered in order to remove particles and other coarse material. Thesolution was filtered first through a 50-μm filter and then through a25-μm filter.

Thereafter, the solution was treated in an ultrafiltration apparatusHSK131 from Alfa Laval, having membranes from Koch with a cut-off of5000u. In this apparatus, the solution was concentrated, and salts andpeptides were removed. After ultrafiltration, the solution now having adry solids content of 20% was subjected to an ion-exchange treatment inorder to remove most of the remaining salts. Then, the solution wasfiltered in three steps.

In the first step, the solution was filtered in order to remove anyremaining fat. In the second step, the solution was filtered throughactive carbon in order to remove colour and improve the taste and smell.In the third step, the solution was filtered through a polishing filterin order to achieve final clarity. Thereafter, the solution was cooledso that the gelatin gelled, and so-called noodles then formed in ascraped-surface heat exchanger, e.g., ALFA LAVAL-CONTHERM®, and dryingwas carried out. The resulting gelatin had a Bloom number of 290, aviscosity of 42.3 mPs, and a clarity of 21 NTU, as measured by means ofa Hach Ratio Turbidimeter. NTU, which is a measure of clarity, standsfor Nephelometric Turbidity Units. The isoelectric point IEP was 7.3.

EXAMPLE 2

Bone of food quality obtained from slaughterhouses was defatted in anAlfa Laval Centribone process. By means of a hydrocyclone, the bonematerial was separated into two fractions, one containing most of thebone and one chiefly composed of softer material. The bone fraction wasused in this Example.

The bone was mixed with water to a slurry having a dry solids content ofabout 20% and was ground to a particle size of about 1-2 mm in a Simoindustrial mill. The slurry was then transferred to a Dorr-OliverSupraton mill equipped with conical grinding gear. After this treatment,the average particle size was about 200 μm. The slurry was furthertreated in a Sussmeyer pearl mill to a final average particle size ofabout 20 μm. The pH of the slurry was adjusted to 4 by means ofphosphoric acid, and the temperature was adjusted to 100° C. in an ALFALAVAL-CONTHERM®. The residence time was 5 min. The pH was then adjustedto 5.5 by means of calcium dihydroxide, and the temperature was adjustedto 60° C. Thereafter, the treatment proceeded as in Example 1 above.

In this Example, 85% of the collagen was converted to gelatin having aBloom number of 310 and a viscosity of 46.3 mPs.

EXAMPLE 3

In this Example, the inventive method was tested on a laboratory scale.The tests were carried out with and without an enzyme treatment, andwith and without ultrafiltration of the gelatin solution. * indicatesadditional steps of enzymatic treatment.

1) 2 kg of bone meal (particle size of 40-125 μm) was mixed with 6 kg ofice water to a slurry.

2) The bone meal was partially demineralised by means of concentratedphosphoric acid to a pH of 3.

3) * The pH was adjusted to about 7.

4) * ESPERASE® was added (0.5%), and the slurry was agitated over night.

5) The pH was adjusted to 3.5.

6) Extraction was performed by batchwise (2 l) heating to 90° C. in amicrowave oven (about 15 min).

7) The solution was neutralised by means of Ca(OH)₂, and was centrifugedand filtered on cellulose with the aid of filter equipment.

8) Part of the solution was dried at once, and part of the solution wassubjected to ultrafiltration.

9) The yield, the Bloom number, the viscosity, the clarity and the ashcontent were determined.

The results of these tests are accounted for in the Table below.

                  TABLE    ______________________________________    The results of tests with and without enzyme treatment,    as well as with and without ultrafiltration (UF), of the    gelatin produced.                                       Ash               Bloom    Viscosity                                 Clarity                                       content                                             Yield*    Test       number   (mPs)    (NTU) (%)   (%)    ______________________________________    Without enzyme                302**   --       --    18.8    Without enzyme +               300      37       150    3.9  73    UF    Enzyme     182      29       --    12.2    Enzyme + UF               256      35       249    6.8  87    ______________________________________     *Total yield after 2 extraction stages.     **Bloom number measured on half the amount.

What is claimed is:
 1. A method for producing gelatin from acollagen-containing raw material without a requirement for ademineralization step, said method consisting essentially of the stepsofa) grinding the raw material to a particle size not exceeding 1 mm, b)mixing the ground material with water to form a slurry, c) adjusting thepH of the slurry to 2-5 and adjusting the temperature of the slurry to60°-130° C. for a time between 1 second and one hour, d) adjusting thetemperature of the slurry to 100° C. or below, e) separating the slurryinto a gelatin-containing liquid portion and a solid residue, f)increasing the pH of the slurry or the liquid portion before or afterthe separation of step e), and g) recovering the gelatin from the liquidportion,wherein steps a) to f) are performed with essentially no removalof process water.
 2. The method as set forth in claim 1, wherein the rawmaterial is wet-ground or dry-ground.
 3. A method as set forth in claim1, which is implemented in continuous or semicontinuous fashion orbatchwise.
 4. The method as set forth in claim 1, wherein the rawmaterial is ground to a particle size of<about 300 μm.
 5. The method ofclaim 4 wherein the particle size is<100 μm.
 6. The method of claim 5wherein the particle size is<40 μm.
 7. The method as set forth in claim1, wherein the slurry in step c) is treated with an acid to attain a pHof 3.5-5.
 8. The method as set forth in claim 7, wherein the acid isselected from the group consisting of HCl, H₃ PO₄, HNO₃, CH₃ COOH and H₂SO₄, and mixtures thereof.
 9. The method as set forth in claim 1,wherein the slurry in step c) is heated to a temperature of about80°-110° C.
 10. The method as set forth in claim 1, wherein thetreatment time in step c) is 5-40 min.
 11. The method as set forth inclaim 1, wherein the raw material is defatted prior to grinding.
 12. Themethod as set forth in claim 1, wherein the gelatin from the liquidportion is recovered by filtering in one or more steps.
 13. The methodof claim 1 wherein pH is adjusted prior to temperature in step c). 14.The method of claim 1 wherein temperature is adjusted prior to pH instep c).
 15. A method as set forth in any one of claims 2-7, 9-10, or11-6 or 1-14, wherein the treatment time in step c) is 10-30 minutes.